The present invention relates to a throttle valve position-detecting device for a vehicle for detecting a position of a throttle valve in a throttle body provided for an internal combustion engine mounted on the vehicle, e.g., the engine for propelling the vehicle.
In the past, there has been provided a conventional throttle valve position detecting device comprising a first rotary element having a projection, this first rotary element being fixed to a throttle shaft, and a throttle position sensor for detecting the position of a throttle valve from the position of the projection. The conventional throttle position sensor comprises a rotary shaft having the same rotary axis as the throttle shaft, a second rotary element fixed to the rotary shaft and engaging the projection of the first rotary element to be rotated by the projection, a coil spring to press the second rotary element to the projection, and a detecting circuit for electrically detecting the position of the throttle valve from rotation of the rotary shaft. The throttle shaft has a butterfly valve as a main part of the throttle valve and intersects a throttle bore through which air is lead to the internal combustion engine. The throttle shaft is supported by a bearing provided in a throttle body in which the throttle bore is formed.
When such a prior art detecting device as described above is used for a long time, the clearance between the throttle shaft and the bearing becomes large by virtue of abrasion therebetween. As the butterfly valve in the throttle bore strongly receives a negative pressure from the internal combustion engine during the idling condition thereof, the throttle shaft moves downwardly as permitted by the clearance.
In the above-mentioned conventional detecting device, the moving direction of the throttle shaft is perpendicular to a contact face of the second rotary element and the projection of the first rotary element during the engine idling condition, that is, the crossing angle of the moving direction of the throttle shaft and the rotary power transmitting direction from the projection of the first rotary element to the second rotary element during the engine idling condition is 0 degrees. Therefore, as the projection of the first rotary element causes the second rotary element to move in accordance with the moving of the throttle shaft, the throttle position sensor no longer properly detects the idling position of the throttle valve irrespective of the engine idling condition.